MMIC technology is commonly used for making microwave circuits for processing microwave signals, i.e. signals typically lying in the frequency range 1 GHz to 50 GHz or more.
FIG. 1 shows an example of a known power amplifier in MMIC technology. The amplifier of FIG. 1 has four transistors 1 to 4 operating in parallel and fed by symmetrical voltage divider circuits; they output signals to voltage combiner circuits that are likewise symmetrical. In the example of FIG. 1, the amplifier has two input divider stages, and two output combiner stages. The input signal to the amplifier is applied to an input terminal 5, and is then divided into two signals that are equal in amplitude and in phase in two branches 6 and 7. The signals in each of these branches are in turn separated into two identical signals which are applied to the grid buses of the transistors 1 to 4. More precisely, the signals in branch 6 are separated into two signals on branches 8 and 10, which are applied to the grid buses of transistors 1 and 2; the signals on branch 7 are separated into two signals on branches 9 and 11, which are applied to the grid buses of transistors 3 and 4. At the outputs from the transistors, the circuit is symmetrical about a line through the transistors. The signals delivered by the drain arrays of the transistors 1 and 2 to branches 14 and 16 are combined and applied to a branch 18 while the signals supplied by the drain arrays of the transistors 15 and 17 are combined and applied to a branch 19. The signals from the branches 18 and 19 are combined and constitute the output signal on terminal 20.
The circuit of FIG. 1 presents the advantage of being very simple in design, with the signals being easy to divide and to combine. Nevertheless, it suffers from the drawback of being adaptable only to a number of transistors that is equal to an integer power of 2, four transistors in the example of FIG. 1. This can lead to difficulties when dimensioning the various transistors forming the circuit. In addition, the circuit of FIG. 1 occupies a large area on the circuit-supporting medium.